Braxton Hicks

I’m a first-time, soon-to-be mom and am29 weeks pregnant. At my last appointment my doctor told me that I could begin feeling Braxton Hicks contractions are any point in the 3rd trimester, and some women experience them, and some don’t. I am curious as someone who doesn’t have a full understanding of them as to what they feel like and what to expect? From research I’m gathering that they are not really painful, but just uncomfortable? If you had to try to explain them in a most simplified way, what would that be?